Stable isotopes (δ18O and δ13C) give new perspective on the ecology and diet of Endothiodon bathystoma (Therapsida, Dicynodontia) from the late Permian of the South African Karoo Basin

Abstract The late Permian dicynodont Endothiodon is characterized by its specialized feeding system, most notably manifested in its long rows of post-canine teeth and corresponding keratinous surfaces. This specialisation has fuelled discussion of not only the masticatory biomechanics in Endothiodon but also of its diet and ecology. To shed light on the latter two, we compared the oxygen (δ18Op) and carbon (δ13Cc) stable isotope compositions of Endothiodon tooth and bone apatite with those of the co-occurring dicynodont Tropidostoma, another late Permian dicynodont of similar size. Preliminary results indicate that Endothiodon had significantly lower ratios for stable isotopes of both oxygen and carbon. The δ18Op values from Endothiodon suggest that its lifestyle was more water-dependent (i.e. obligate drinker) than Tropidostoma, pointing to the possibility of a semi-aquatic ecology, whereas δ13Cc values suggest that Endothiodon had a diet primarily comprising riverine vegetation, with the possibility that juveniles consumed terrestrial insects. The data suggest a negligible role for roots, seeds, or algae in the diet of Endothiodon.